This invention relates to scanning microscopes used for imaging the topography of surfaces and, more particularly, to a scanning ion conductance microscope comprising, a reservoir holding a sample to be scanned therein; a micropipette having a tip communicating with a shaft; an electrolyte solution disposed within the reservoir covering the sample and disposed within the tip and shaft of the micropipette; a first microelectrode disposed in the shaft in electrical contact with the electrolyte therein; a second microelectrode disposed in the reservoir in electrical contact with the electrolyte therein; scanning means for scanning the tip of the micropipette over a top surface of the sample in a scanning pattern; voltage means for applying a voltage across the first and second microelectrodes; current means for measuring the current flowing between the first and second microelectrodes and for supplying an indication of the current at an output thereof; and, control logic means having an output connected to the scanning means and an input connected to the output of the current means for causing the scanning means to set the height of the tip at a desired distance above the top surface and for outputting data of interest related to the top surface as it is scanned.
The family of scanning probe microscopes that have been introduced to the scientific community of recent years is broadening the frontiers of microscopy. As typified by the greatly simplified general example of FIG. 1, these microscopes scan a sharp probe 10 over the surface 12 of a sample 14 to obtain surface contours, in some cases actually down to the atomic sale. The probe 10 may be affixed to a scanning mechanism and moved in a scan pattern over the surface 12 or alternately (and equally effectively because of the small sizes involved) the probe 10 may be stationary with the sample 14 mounted on a scanning mechanism that moves the surface 12 across the probe 10 in a scanning pattern. The point 16 of the probe 10 rides over the surface 12 as the probe is moved across it as indicated by the arrow 18. As the point 16 follows the topography of the surface 12, the probe 10 moves up and down as indicated by the bi-directional arrow 20. This up and down movement of the probe 10 is sensed to develop a signal which is indicative of the z directional component of the 3-dimensional surface 12.
The use of a piezoelectrically driven tube to affect the x-, y-, and z-directional movements employed in the scanning process is generally accepted in such devices and such well known equipment is preferred for use in the scanning aspects of this invention as well. Various methods are employed to sense the vertical movement of the probe 10. Where the sample 14 is of an electrically conductive material and the scanning is conducted in a non-conductive environment such as air, current flow between the probe point 16 and the surface 12 can be employed to control the vertical position of the probe 10. The vertical control signal then supplies the z-directional component. For non-conducting materials it is more common to measure the vertical deflection of the probe 10 directly in order to develop the z-directional component.
While the contact type of scanning probe microscope as described above works well in certain environments, in other environments it is virtually worthless. This is particularly true where the sample is of a soft material which cannot be subjected to the contacting probe described above. While the biasing force of the probe against the surface of the sample in such prior art apparatus is exceedingly small, it is still there and the probe itself is quite sharp in order to follow the contours demanded of it. Accordingly for example, if a soft membrane is contact scanned, it is torn by the probe.
Additionally, despite their various attributes, such prior art scanning microscopes can only supply a visualization of the surface topography. They cannot show, for example, ion flow capabilities of and through the surface under examination.
Wherefore, it is an object of the present invention to provide a non-contacting scanning microscope which can be used to display an indication of the surface topography of materials which cannot be scanned with a contacting probe.
It is another object of the present invention to provide a scanning microscope which can be used to display an indication of ion flow capabilities of and through a surface under examination.
Other objects and benefits of this invention will become apparent from the description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.